(CNN) -- Cyberattacks are an increasing threat at home, while extremists continue to make inroads in Middle Eastern and African countries that are in transition after the Arab Spring, according to the U.S. intelligence community's worldwide threat assessment.

The annual document was released Tuesday.

"Threats are more diverse, interconnected and viral than at any time in history," Director of National Intelligence James Clapper said in testimony prepared for the Senate Select Committee on Intelligence.

For the first time, the emphasis of the report was on cyberthreats, in the form of cyberattacks or cyberespionage.

"Attacks, which might involve cyber and financial weapons, can be deniable and unattributable," Clapper writes in the document. "Destruction can be invisible, latent and progressive."

The Internet is increasingly being used as a tool both by states and by nonstate actors, such as terrorist groups, to achieve their objectives, the report says.

However, there is only a "remote chance" of a major cyberattack on the United State that would cause widespread disruptions, such as regional power outages, the report says. Most countries or groups don't have the capacity to pull it off.

The report names China and Russia as two of the most "advanced cyber actors," but says they are unlikely to launch an attack.

The current risk is that isolated states or groups might attack the United States with less sophisticated cyberattacks, the report says.

Already, foreign intelligence and security services have "penetrated numerous computer networks" in the United States belonging to the government and private sector alike, the report says.

Although classified networks have been targeted, the majority of these attacks have involved unclassified networks, it states.

The United States has enjoyed a technological edge over other nations, but advances in information technology and business practices are evening the playing field, according to the report.

"This is almost certainly allowing our adversaries to close the technological gap between our respective militaries, slowly neutralizing one of our key advantages in the international arena," it states.

The threat assessment describes an environment where jihadist terrorists are increasingly decentralized, creating challenges for the prevention of attacks.

Many of these groups have gained a foothold in the Arab Spring countries, where a spike in threats to U.S. interests has been recorded, the report says.

"The dispersed and decentralized nature of the terrorist networks active in the region highlights that the threat to U.S. and Western interests overseas is more likely to be unpredictable," it states.

It cites the Benghazi, Libya, attack that killed four Americans and an attack on an Algerian oil field as examples of how splinter groups or individuals with jihadist sympathies can act, even without direction from higher in the terrorist chain.

While these splinter groups pose a greater threat, the "core" of al Qaeda remains weakened, according to the report.

The terrorist group's losses in 2012, coupled with earlier defeats, "have degraded core al Qaeda to a point that the group is probably unable to carry out complex, large-scale attacks in the West," it says.

One of the most active al Qaeda groups is al Qaeda in the Arabian Peninsula, whose objectives include targets on U.S. soil, the report says.

Nuclear threats from Iran and North Korea remain a priority, though the report does not say with certainty what those countries' end goals are.

Iran has the scientific and technical capacity to eventually build nuclear weapons, the report says, adding that it is not known if Iran will ever decide to produce any.

North Korea's nuclear weapons pose a "serious threat," the report says, but it admits the United States has limited intelligence about the regime's thresholds for using those weapons.

The report says the Syrian government maintains a stockpile of chemical weapons which could produce mass casualties if used.

"We assess that an increasingly beleaguered regime, having found its escalation of violence through conventional means inadequate, might be prepared to use (chemical weapons) against the Syrian people," the intelligence assessment says.

In Afghanistan, coalition forces have made gains, the report says, but it is fragile in areas where security is being turned over to the Afghans.

"We assess that the Taliban-led insurgency has diminished in some areas of Afghanistan but remains resilient and capable of challenging U.S. and international goals," the report states.